Build system changes

[Thomas Klausner <tk%giga.or.at@localhost>]

Hi!

For a long time, we have been maintaining two build systems for
libzip: one based on autoconf/automake and one using CMake.

The maintenance of two systems lead to various items not being
correctly handled in both systems, due to oversight and errors. And it
came with a cost in time and effort.

For that reason, we have retired the autoconf/automake based build
system and will now only support the CMake one.

The basic usage then is

    mkdir build
    cd build
    cmake ..
    make
    make test
    make install

For more details, see the INSTALL.md[1] file.

If you have questions that are not answered by this, let us know!
 Thomas


https://github.com/nih-at/libzip/blob/master/INSTALL.md